Usually the engine case "stuck" in place and to release it you need a special force. If you did not use force to separate the engine case from its place and it stays "stuck", then there is no problem. Tighten the screws back in place in crisscross pattern.
If there will be a leak then open it, carefully and gently remove the old gasket without damaging the aluminum case, take a New Gasket wet from engine oil, and tighten the screws in crisscross pattern.
After first activation wipe off the oil residue.
Be Careful not to tighten the screws too tightly to prevent damage to the aluminum threads in the engine case!!!